(1) Field of Invention
The present invention relates to microelectronic array formation, and more particularly, to a method for forming a microelectronic array that can conform its shape to an arbitrary three-dimensional shape.
(2) Description of Related Art
Electronics and/or semiconductors are typically formed as flat wafers. In some circumstances, it may be desirable to form a semiconductor as a curved structure. However, current semiconductor technology is limited in its ability to form curved structures containing high densities of active components. There are known techniques that employ simple bending procedures of a thinned crystalline material, or segmenting the structure into sub-arrays to allow for curving of the arrays. By way of example, Dr. James Gregory of the Massachusetts Institute of Technology (MIT) Lincoln Laboratory (LL), used a bending procedure to bend thin charge coupled device (CCD) arrays (details given below). MIT's Lincoln Laboratory is located at 244 Wood Street, Lexington, Mass., 02420-9108, United States of America (U.S.A.).
Dr. James Gregory has demonstrated the basic technology for deforming thinned CCD arrays into cylindrical and spherical focal planes. In his work, an integrated circuit on a curved surface is produced from a circuit on a planar wafer by thinning the substrate wafer and deforming the thinned membrane into a curved shape.
LL has fabricated, thinned, and deformed CCDs, and evaluated the CCDs for electrical and optical performance. In his work, Dr. Gregory discussed the benefits of curved focal surfaces, which occur naturally in many lens systems. A benefit identified by Dr. Gregory is that the optical performance can be improved while eliminating corrective elements to reduce system complexity. LL has fabricated and tested a CCD petal chip that can be wrapped around a spherical section. LL also explored creating a Si mesh with conductive elements and deforming this mesh and populating it with discrete optical detectors.
Spherical curvature of semiconductor devices on a Kapton film has been demonstrated by a group at Princeton University (P. I. Hsu, R. Bhattacharya, H. Gleskova, M. Huang, Z. Xi, Z. Suo, S. Wagner, and J. C. Sturma, Applied Physics Letters, 81, 1723 (2002)). Princeton University is located at Princeton, N.J. 08544, U.S.A. Thin film transistors on a 6 centimeter (2.36 inches) diameter Kapton film were deformed using a pressurized gas. The Princeton group reported a limited curvature of one steradian (˜7% of a sphere's surface area). While a curvature occurred, one steradian is insufficient if attempting to conform the semiconductor device to a sphere.
Additionally, U.S. Pat. No. 6,455,931, issued to Hamilton, Jr. et al. (hereinafter “the Hamilton patent”), discloses a micro-electronic array structure having substrate islands. The Hamilton patent discloses forming a thinned material between the islands, so that the micro-electronic array structure can be bent around a curved object.
In the prior art discussed above, the methods for covering arbitrary shapes with a semiconductor material typically involve stretching a flexible film. A problem associated with stretching flexible film is that electrical resistance degradation occurs between the metals used to interconnect the discrete devices. In approaches involving stretching of the material, the interconnects are pulled in tension and the resistance increases rapidly. Metal in tension is also more likely to fail from cracking.
The approaches described above are limited in the variety of shapes that can be conformed to and their general applicability to a wide set of device or sensor technologies. Additionally, the prior art relies on deforming the active device itself, which requires thinning the initially rigid material for curvature to be accomplished. Bending or deforming the active components can introduce serious performance degradation by increasing the resistance between the metal interconnects.
Thus, a continuing need exists for a technique to conform a micro-electronic array to arbitrary shapes that allows for a high degree of curvature or surface coverage, and that does not cause performance degradation.